The present invention relates to an astigmatism correction technology for a projection image display apparatus which irradiates light from a light source onto such a light valve as that of a liquid-crystal panel, forms optical images in response to image signals, and provides an enlarged projection of the images.
Conventional technologies for splitting polarized light, related to the present invention, include those described in Japanese Patent Application Laid-Open Publication Nos. 2001-56449 and Hei 10-55037. In addition, conventional related technologies for correcting astigmatism include those described in Japanese Patent Application Laid-Open Publication Nos. Hei 5-313119, Hei 9-114021, and 2000-111862.
Japanese Patent Application Laid-Open Publication Nos. 2001-56449 and Hei 10-55037 each disclose an arrangement with three sets of reflection-type light valves and polarization beam splitter, each set being for red (R), green (G), and blue (B), wherein light components of each of the R, G, and B colors are color-synthesized via a cross dichroic prism. Polarized light is split using, for example, a polarized beam splitter (PBS) prism with PBS formed as a dielectric multi-layer film on the interface between two rectangular prisms, or a wire-grid polarized-beam splitter having a wire-grid-structured diffraction grating formed on a light-transmissive substrate.
Japanese Patent Application Laid-Open Publication No. Hei 5-313119 discloses a technology in which a flat-plate-like dichroic mirror for conducting color syntheses is transformed into a wedge-like dichroic mirror to correct the astigmatism occurring when light passes through the flat-plate-like dichroic mirror. Japanese Patent Application Laid-Open Publication No. Hei 9-114021 discloses an arrangement in which a field lens having an astigmatism correction function is disposed at the exit side of a liquid-crystal panel to correct astigmatism due to the use of a dichroic mirror. Japanese Patent Application Laid-Open Publication No. 2000-111862 discloses a technology in which the thickness and inclination of the flat-plate-like dichroic mirror for the color components of light that is disposed on a front face of a panel and acts as a polarizer/analyzer, are adjusted to correct astigmatism due to the use of the dichroic mirror.